1. Field of the Invention
This invention concerns a smelting method to produce very pure iron or various iron family metals from ores which contain iron, nickel, cobalt, etc., by means of hydrometallurgy.
2. Background Information
Among those means to produce iron from iron ore in great quantity, the blast furnace process is usually adopted to the current and modern iron-making industry. In the case of the blast furnace process, a mixture of iron ore, fluxes, etc. are melted and reduced, then produced molten iron and slag are separated due to the difference of their specific gravity, and iron is extracted.
On the other hand, besides the blast furnace process, there are many so-called direct iron-making processes to extract iron from iron ores. For example, they are the Armco process, the treatment of Laterite and the Hoganas process.
In the case of the blast furnace process, however, a furnace of very large volume equipped with many large accessories is necessary in order to heat and melt the mixture of iron ore, fluxes, etc. with high thermal efficiency at an elevated temperature, so that a high construction cost is necessary. Since the iron produced in this case usually contains 2% or more of carbon, phosphorus, sulfur, etc. the iron is refined once again to make steel.
In contrast thereto, the reduced iron produced by the Armco process, the treatment of Laterite, etc. mostly contains SiO2, Al2O3, etc. that are originally included in the iron ore. In the case of the Hoganas process, it is impossible to completely remove SiO2, Al2O3, etc. that are included in the iron ore. Accordingly, in order to completely remove SiO2, Al2O3, etc. from the reduced iron, it is necessary to carry out refining once again, as in the case of the blast furnace process.
As such, in order to obtain very pure iron which contains no SiO2, Al2O3, etc. from the iron ore, it is required to provide remelting and refining facilities, which results in a high construction cost. Heretofore, there has not been a wet smelting technique for mass-production which does not need such melting and refining process.
The present invention was developed intending to solve the aforementioned problems, and also to provide a specific refining method by hydrometallurgy, thereby very pure iron or various iron family metals are obtained from ores containing iron family metals.
The inventor made an intense study to solve the aforementioned problems. As a result of the study, it was discovered that if ores containing iron family metals are subjected to an artificially hastening treatment relating to the leaching of iron family metals into acid, namely, an xe2x80x9caccelerated weathering treatmentxe2x80x9d, those metals are eluted easily into acid, whereby a hydrometallurgy method carried out on iron family metals is realized.
The present invention was achieved based on the aforementioned knowledge, and it comprises specific features as set forth in the following procedures:
(a) a grinding process wherein ores containing iron family metals are pulverized into fines of 25 mesh undersize (hereinafter referred to as the xe2x80x9cpulverized orexe2x80x9d; the xe2x80x9corexe2x80x9d is a kind of native mineral, but it does not cover processed resources such as iron bearing byproducts of the chemical industry, etc. (e.g., sludge, cinder, residue, or gangue)),
(b) a leaching process wherein iron family metals in the pulverized ore are eluted into at least one inorganic acid, such that the pulverized ore is immersed into an inorganic dilute acid having a concentration of 1N to 8N, preferably 2N to 6N (hereinafter referred to as the xe2x80x9cinorganic acidxe2x80x9d),
(c) a separation process to obtain a filtrate and gangue individually by filtering the mixture of residue and inorganic acid which contains the eluted iron family metals discussed above,
(d) a precipitation process of a hydroxide of the iron family metals by the addition of an alkali to the filtrate obtained in the preceding step, and a filtration process applied to the suspension composed of the aforementioned hydroxide to collect a hydroxide of the iron family metals, and
(e) reducing process of which the collected hydroxide is heated at a temperature of 600 to 950xc2x0 C. for 5 minutes or longer in a reducing atmosphere immediately after a pre-reducing process carried out at a temperature of 400 to 500xc2x0 C. for 5 minutes or longer in the same reducing atmosphere.
The present invention preferably comprises the specific feature of which a hydroxide of the iron family metals is rinsed with a sufficient amount of warm water (water at a temperature of 40 to 60xc2x0 C., which is defined in JIS K0050 (1991)) before the reducing treatment thereof.
In order to collect an iron hydroxide, usually a centrifugal machine is used for filtration. However, the collected hydroxide is not discharged from the machine right after filtration, but warm water is added into the machine, and it is driven once again. After that the iron hydroxide is taken out. This is explained in more detail as follows.
In the neutralization process, a hydroxide (solid) of iron or an iron family metal and a liquor are produced. The liquor includes such salt(s) as Na2SO4 and NaCl. The kind of salt(s) depends on the kind of alkali used for neutralization.
A first separation by filtration involves charging the mixture of the hydroxide and the liquor described above into a centrifugal separator, sufficiently separating the hydroxide and the liquor, and stopping the revolution of the separator at once. At this moment, the liquor is discharged while the hydroxide remains in the separator. The dehydrated hydroxide thus obtained still includes some of the salt(s) discussed above.
A second separation by filtration involves pouring warm water into the hydroxide in the separator, and driving the separator once again in such manner, at first, slowly, then rapidly. As a result of this operation, the salt(s) absorbed in the hydroxide is eluted into the warm water and separated therefrom. After completion of this separation, the hydroxide from the separator is discharged.
The addition of warm water causes elution of some of the hydroxide. To prevent a decrease of the recovery ratio of iron, the addition of warm water is restricted once.
The present invention preferably comprises the following specific feature: between the steps (a) and (b), the pulverized ore prepared by step (a) is subjected to reducing such that it is heated at a temperature of 600 to 1100xc2x0 C. for 5 minutes or longer. Further, it is preferable that at the time of reducing, at least any one among an oxide, a hydroxide, or a carbonate of zinc, calcium, lead or potassium is added as a catalyst. Furthermore, after the reducing treatment, the reduced ore is preferably magnetically separated.
Preferably, the present invention further comprises the following specific feature: between the steps (b) and (c), the pulverized ore ground to the desired size as described hereinabove is agitated successively for 30 minutes or longer, as it is immersed in the inorganic acid of the aforementioned concentration.
Furthermore, the invention preferably comprises the following specific feature: between steps (b) and (c), the pulverized ore ground to the desired size as described hereinabove is heated for 1 minute or longer, as it is immersed in the inorganic acid of the aforementioned concentration.
The invention preferably comprises the following specific feature: between the steps (b) and (c), the pulverized ore ground to the desired size as described hereinabove is agitated successively for 30 minutes or longer and also heated for 1 minute or longer, as it is immersed in the inorganic acid of the aforementioned concentration. In this case, the agitating is not always required to be before the heating.
As described hereinabove, according to the present invention a wet smelting process is provided wherein very pure iron or various iron family metals are obtained very economically in a large quantity from ores which contain iron family metals, which is in contrast to the blast furnace process or the like which need high construction expenses. Further, the temperature of the heating process for reducing the collected hydroxide of the iron family metals is below the melting point of iron family metals. Also an inorganic acid is used for elution of iron family metals from ore and a reducing agent used for the reducing is cheap and readily obtainable, whereby the production cost will be cheaper than that of other processes applied heretofore.
According to iron and steel making processes applied heretofore, the use of high quality iron ore is always a precondition, while in the process of the present invention, not only high quality iron ores, but also poor quality iron ores that are abundant resources may be used. Moreover, strongly coking coal necessary for the pig iron process is not needed.
In addition, since the form of very pure iron or various iron family metals obtained by the process of the present invention is powdery, they are able to be subjected to sintering using an appropriate mold as it is, without the addition of additional elements to the powder. Accordingly, a working, a heat treatment, or the like which were heretofore essential processes, may be omitted in the present invention, and also various forms of product are able to be manufactured economically and directly from the powder.
As discussed hereinbefore, according to the present invention, various excellent commercial advantages are provided.
When the usual hydrometallurgy technique, which intends to remove such inclusions as SiO2 and Al2O3 contained in ores, is applied, normally it is very difficult or an extremely long time to elute the iron family metals into at least one inorganic dilute acid is required, even though such depends on the mineralogical structure of the ores.
Therefore, in the present invention, firstly, an ore is ground to 25 mesh undersize, and the pulverized ore is immersed into at least one inorganic acid. Accordingly, iron family metals in the ore are able to be eluted into the inorganic acid. If the size of the said ore is coarse, namely 25 mesh oversize, or the concentration of the inorganic acid is less than 1N, elution of iron family metals will need an extremely long time, so that those conditions are impractical.
As to the ores useful in the present invention, most ores which contain iron family metals are available. They are, for instance, iron rich ores that include hematitic ore, magnetitic iron ore, limonitic, etc., low grade ores that are Jarosite, etc., and Laterite. Depending on the composition of the ore, pure iron or metals which contain iron, nickel, cobalt, etc., are obtainable.
Grinding of the ores is easily realized with usual jaw crushers, ball mills, etc.
Pertaining to the inorganic acid used for elution of the iron family metals from the ores discussed hereinabove, hydrochloric acid, sulfuric acid, sulfurous acid, aqua regia, etc. can be used.
Subsequently, the aforementioned mixture of residue and inorganic acid which contains eluted iron family metals described above is filtered to separate a filtrate and gangue. After that, an appropriate alkali is added to the filtrate separated from the gangue, whereby a hydroxide of the iron family metals is precipitated. Then, the precipitated hydroxide of the iron family metals is collected by filtrating of the suspension which contains the hydroxide thereof.
As to the alkali used for formation of the hydroxide of iron family metals, limestone, burnt lime, slaked lime, as well as sodium hydroxide, potassium hydroxide, calcium hydroxide, aqueous ammonia, and the like, can be used.
As the next procedure, the collected hydroxide of the iron family metals is converted to an easily reducible one, when it is pre-reduced by heating at a temperature of 400 to 500xc2x0 C. for 5 minutes or longer in a reducing atmosphere, then it is subjected-to reducing, that is heating at 600 to 950xc2x0 C. for 5 minutes or longer. As such, a powdery very pure iron or various iron family metals is attainable.
When the temperature of pre-reducing, that is a process to convert the hydroxide of the iron family metals or a dried hydroxide thereof to an easily reducible one, is below 400xc2x0 C., or above 500xc2x0 C., an ensuing reduction which will be carried out at a temperature of 600 to 950xc2x0 C. becomes difficult. Further, if the reducing temperature is below 600xc2x0 C., it is not practical, since a long time is necessary for reducing. On the other hand, when the reducing temperature is above 950xc2x0 C., a produced pure iron or various iron family metals tend to combine by sintering so that it becomes difficult to maintain a powdery state of product, whereby some serious problems for the usage of the product will occur.
The duration time for pre-reducing and reducing discussed above will be at least 5 minutes, respectively. If both or either of them are shorter than 5 minutes, the pre-reducing and/or the reducing are liable to be insufficient.
As to the reducing atmosphere for the pre-reducing and reducing of the hydroxide of the iron family metals, H2 gas, HNX gas, producer gas mainly comprising CO and H2, CO gas, ammonia gas, coke oven gas, natural gas, blast furnace gas, water gas, methane gas, and the like can be used. In this regard, when gases containing carbon are used, they are liable to decompose to C, H2, O2, etc. at an elevated temperature. Accordingly, it is recommendable to use a catalyst for preventing such decomposition.
Prior to the reducing of the hydroxide of the iron family metals, if rinsing with warm water is carried out, salt(s) adhered on the iron family metals will be removed, therefore, the purity of pure iron or iron family metals obtained by reducing will be much improved. If salt(s) adhere on the hydroxide of the iron family metals, the solid subjected to reducing tends to sinter at a lower temperature, so that it becomes difficult to maintain a powdery state of the product.
Prior to immersing the ore which contains the iron family metals ground to 25 mesh undersize into the inorganic acid, if the pulverized ore is subjected to a reducing treatment, heated at a temperature of 600 to 1100xc2x0 C. for 5 minutes or longer, elution of iron family metals into the inorganic acid will be remarkably hastened. In this regard, if the reducing temperature is below 600xc2x0 C. or above 1100xc2x0 C., and the duration time for reducing is shorter than 5 minutes, it is very difficult to attain the desired reducing effect. The above described matter is also a part of an xe2x80x9caccelerated weathering treatmentxe2x80x9d. In this regard, the metallization ratio is not always required to be 100%. In addition, as to the reducing treatment, any widely known process may be applicable.
The accelerated weathering treatment includes the following treatments:
(i) grinding of ores as fine as possible to obtain the pulverized ore,
(ii) reduction roasting of the pulverized ore, and
(iii) addition of catalyst(s) to the pulverized ore right before the reduction roasting.
In this respect, the application of treatments (ii) and/or (iii) is determined according to the kind of the ore.
At the time of reducing of the ore which contains the iron family metals ground to 25 mesh undersize, if at least any one kind of catalyst such as an oxide, a hydroxide or a carbonate of zinc, calcium, lead or potassium is added thereto, the elution of the iron family metals into the inorganic acid will be additionally hastened.
The reducing treatment described above may be achieved by heating the ore in a non-oxygenating atmosphere with charcoal, coke, coal, sawdust;, cut paper, etc. or otherwise in a reducing atmosphere such as H2 gas, HNX gas, producer gas mainly comprising CO and H2, CO gas, ammonia gas, coke oven gas, natural gas, blast furnace gas, water gas and methane gas.
As to the ore which contains iron family metals ground to 25 mesh undersize, if it is subjected to a reducing treatment and a magnetic separation prior to immersing it into the inorganic acid, not only is the consumption of acid and alkali saved, but also the purity of produced pure iron or various iron family metals will be further improved.
The ore which contains the iron family metals is ground to 25 mesh undersize and reduced without a catalyst, then the reduced pulverized ore is immersed into the inorganic acid to elute the iron family metals. Next, the ore described above is agitated successively for 30 minutes or longer, or heated at a temperature within the range of 70 to 110xc2x0 C., preferably 95 to 100xc2x0 C., for one minute or longer, or both of such treatments are combined and implemented regardless of the order, as the ore is immersed into the inorganic acid, whereby the reaction time of the iron family metals and the inorganic acid will be remarkably reduced. The heating, in this case, is conducted with boiling water, super-heated steam, hot ceramics which are acid proof and heat resistance, etc.
In the preceding case, a catalyst is not added. Accordingly, the metal in a metallic compound contained in a catalyst is not captured in the product, therefore, the purity of produced very pure iron or various iron family metals will be improved.